70 CALIFORNIA ACADEMY OF SCIENCES. 



be constantly pushed ahead by katabolism and drag his 

 mate after him. Thus, in the case in point, suppose 

 the following proportions of color existed in a pair of 

 these ground squirrels: 



MALE. FEMALE. 



Brown 



Black .... .... 



White 



In accordance with the law of mutual transmission 

 the two sexes are approaching the average: brown 15, 

 black 50 and white 35. As the first ratio had been ad- 

 justed by the difference in metabolism which is sup- 

 posed to be constant, the real goal toward which the 

 male of the next generation is advancing is shown in 

 the following proportion: 



The male of the second generation would then have 

 the proportion of colors as follows: brown 7.5, black 75, 

 and white 26.25, the black having increased consider- 

 ably. In nature no such rapid increase as this is sup- 

 posed to occur. The conservative law of sexual trans- 

 mission and innumerable limiting and modifying cir- 

 cumstances would retard it. 



After attaining a certain goal it would be impossible 

 for any further intensification to take place in the male, 

 as, for example, when it had become perfectly black. The 

 color of the male then becoming stationary, it would be 

 possible for the female to become more and more like 

 the male in accordance with the law of mixed transmis- 

 sion, the characters of the one sex being transferred to 

 the other. This, apparently, has actually taken place in 



